Present day small computers of the personal and business type commonly include a microprocessor, a keyboard and a video display screen or CRT. One can program the computer to process information entered into the system via the keyboard for display on the CRT. Since the processor usually has only a limited amount of memory, as the user's requirements increase, additional memory capacity is connected to the system.
In several of the present day small computers, including those marketed under the trademarks IBM, TRS and APPLE, the added memory component is a mini-floppy disk (51/4" diskette) drive. The requirement for higher capacity evolved a 51/4 inches Winchester drive which stores the data on a rigid disk. Through custom and usage, these drives have become standards in the industry for such small computer systems. Each is invariably contained in a compact generally rectangular package which is on the order of eight inches long, six inches wide and three one-quarter inches high and it fits in a standard size slot either in the computer terminal itself or in a separate housing associated with the terminal.
Also, it is customary in systems of this type to provide memory redundancy. That is, in addition to a working Winchester disk drive, for example, a second or back-up memory is provided for archival purposes. Information that is stored in the working memory is also stored simultaneously in the back-up memory which is intended to be retained in a secure place for a prolonged period for record keeping purposes.
In the past, some have attempted to store the archival information on a floppy disk. However, in the present state of the art, such disks and their associated drives do not have the capacity to back up the quantity of information stored on current and future 51/4 inches Winchester disks. Accordingly, in many cases, the practice has been to utilize a second Winchester disk drive as the back-up memory. This, however, has turned out to be a relatively expensive practice.